Current Ultra-Wideband (UWB) positioning systems typically generate range information using either a time of arrival (TOA) method or a time difference of arrival (TDOA) method. The TDOA method requires a mobile unit needing ranging information to contact one or more reference units, and receive a response from one or more reference units. The mobile unit then calculates each range measurement to generate its own position based on the round trip time required to send a request and receive a response. TDOA can obtain a high degree of accuracy, but has the disadvantage of requiring the mobile unit to possess a transmitter of sufficient power to contact the reference units in addition to being susceptible to severe accuracy latencies during the round trip. The disadvantage of TDOA is that the transmitter adds to the complexity, the weight, size, and power requirements of the mobile unit.
TOA methods calculate position based only on the elapsed time required for a signal having a time tag to travel from the one or more reference units to the mobile unit. Thus, TOA methods eliminate the need for a transmitter in the mobile unit, allowing the mobile unit to be a purely passive receiving device. TOA methods considerably reduce the complexity, the weight, size, and power requirements of the mobile unit. To achieve a high degree of accuracy in arriving at a position solution, a mobile unit employing TOA methods is dependent upon the reference units' ability to accurately generate the time tag information which is transmitted to the mobile unit. High precision oscillators, such as atomic clocks, are expensive and thus not practical for installations deploying a significant number of reference units. Thus, other means must be implemented to mitigate this problem.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for methods and systems for realizing affordable, high accuracy TOA based UWB positioning systems.